Till now,we have mainly studied about three types of matter i.e. solid,liquids & gas.We know that when we are heating solid substance we get a liquid state.But if we are heating a solid crystal before going into liquid state it will pass through turbid state which has properties of both solid and liquid. This matter is known liquid crystals. Liquid crystal is a matter in a state which lies between solids and liquids.They can flow like a liquid but their molecules are arranged like a solid.
Coming to my topic liquid crystal display i.e LCDs. We all are so close today to these LCD TVs.Now let’s see about its working.LCD TV is made up of large number of small pixels.This pixels are responsible for the formation of image. This pixels can also be called as picture element.Now lets see working of each pixel.
In each pixel at the back there is a light source.In LCD TV fluorescent lamps(CCFL) are used as light source.In front of these light source there are 2 polarizing filters adjusted at an angle of 90 degree.Now what are polarising filters?We know that light waves travel in all possible direction.They travel in horizontal direction and vertical direction.The first polarising filter only allows the horizontal waves of light to pass through it and the second polarising filter only allows the vertical waves of light to pass through it. Now in between this filters there are nematic liquid cystals.
One of the important property of these liquid crystals are they can be aligned when they are kept in electric field or magnetic field.Normally they are twisted so they twist the horizontal waves of light into vertical waves.In front of this polarizing filter there are colour filters coloured red, green and blue.Now when electricity is supplied to nematic liquid crystals they get aligned in same direction,so they will not twist the horizontal waves of light into vertical waves,therefore the second polarising filter will block the horizontal waves and no light will appear on the screen.
Thus the pixel will appear dark.Now if electricity is not supplied to these crystals,they are again in twisted position so they will twist he horizontal waves of light into vertical waves and the vertical waves will pass through vertical polarising filter and light will appear on the screen. Thus if necessary electricity is supplied,we can control the amount of twist i.e the amount of light passing through the liquid crystals.
Thus we get 255 values of red,green and blue respectively.In this way a pixel can produce approx 10 million of colour combinations.This is how a LCD tv works..